Automatic drilling machine



April 7, 1953 `c. M. oLEARY 2,634,099

AUTOMATIC DRILLING MACHINE Filed oct. 1o, 194e l 5 sheets-sheet 1 '23 HYoRoKml-:Tlc 1| ToRoul-z FLUID 8 "24 TRANSMITTER OPERATED soLENom Sgneo OPF-RATED cLuTcH VALVE |65' les' INVENTOR CHARLES M. ol LEARY By /yfma/ D14@ *M ATTORNgYS April '7, v1953 c. M. ofLEARY 2,634,099

AUTOMATIC DRILLING MACHINE med oct. 1o, 1946 5 sheets-sheet 2 INVENTOR. 1, Cif/'Zea' M Zed/ BY i April 1,`1953 C. M. OLEARY 2,634,099

AUTOMATIC DRILLING MACHINE Filed Oct. 10, 1946 5 Sheets-Sheet 5 April 7, 1953 c. M. OL'EARY 2,634,099

AUTOMATIC DRILLING MACHINE Filed Oct. 10, 1946 5 Sheets-Sheet 4 INVENTQR CHARLES M. O'LEARY Bv Mpfo'u,

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Patented Apr. 7, 1953 s UNITED STATES PATENT OFFICE AUTOMATIC DRILLiNG MACHINE Charles OLeary, lios Angeles, Calif. Application october 1o, 1946, serian No. 702,539

l 8 claims.' (o1. Z55-19) Thev present invention relates to rotary well drilling apparatus and constitutes an improvement on applicants copending application, Serial i No. k602,620, filed June 30, 1945, now Patent No. A 2,589,118, on Automatic Well Drilling Mechanism.

This application is based in part on applicants copending application, Serial No. 628,793, now Patent No. 2,582,217, filed November 15, 1945, on

f Hydraulic Drilling Mechanism.

The foregoing application, Serial No. 602,620,

discloses an apparatus for controlling the weight of the drill bit on the formation in such a manner that the drill bit pressure varies in accordance with the torque required to rotate the -drill stem, thus preventing the development of an excessive drill stem twisting force. This result is l achieved by varying the drill stem supporting force exerted by the hoisting drum. An importt ant feature of the mechanism resides in the fact that the percentage rate of change of the drill stem supporting force is less than the corresponding percentage rate of change of the drill stem rotating torque. This result is achieved by -transmitting to the hoisting drum a drill stem supporting torque from one source which remains at aconstant value, independent of drum speed,

and augmenting the drill stem supporting torque by auxiliary means which transmit a torque pro- -portional to the drill stem rotating torque.

It is the general object of the present invention to accomplish the objectsV of the foregoing l application, Serial No. 602,620, by improved mechanisms.

Another object of the present invention is to provide improved means for adjustably controla lower percentage magnitude of change than that of the torque transmitted through said separate mechanism. f

Another object of the invention is to provide lmeans for stopping rotationof the drill stem rwhen the drill stem rotating torque becomes excessive in order to prevent twist-offs.-

Another object of the invention is to provide 4 means effective to prevent rotation vof the upper end of the drill stem `in either direction after the .drill stem rotating torque has reached the predetermined value.

Other objects and advantages of the invention .will become apparent from the following specification, the accompanying drawings and the appgnded claims.. 1 j :f

In the drawings: l

Figure 1 is a diagrammatic view of the preferred form of the present invention;

Figure 2 is a diagrammatic view of the electrical circuit employed in the form of the invention illustrated in Figure 1; f

Figure 3 is a diagram illustrating the performance characteristics of the invention;

Figure 4 is a diagrammatic view of a modiiiecl form of the invention;

Figure 5 is an enlarged View, partly in section, of a portion of the mechanism shown in Figure 4;

Figure 6 is a fragmentary view, partlyin secr tion, of a brake mechanism employed in the form of invention shown in Figure 4;

Figure 7 is a fragmentary section taken on the line 'l-l of Figure 4;

Figure 8 is a diagrammatic view of athird form of the invention; and

Figure 9 is a fragmentary section taken on the line 9 9 of Figure 8.

In accordance with all forms of the present invention, a suitable source of power, such as an internal combustion engine, is connected to the hoisting drum of a well drilling machine by a means which, in connection with the source of power, is capable of transmitting tothe drum a torque that maybe varied and maintained at any desired value, independently of the variations in the unwinding speed of the drum incident to the progress of the well drilling operation. A means responsive to the torque required to rotate the drill stem is provided for controlling the torque delivered to the drum by the variable torque transmitting device, This last means is adjustable not only to vary the general level or `magnitude of the drill stem supporting torque,

but also to vary the percentage rate of change ,in the drill stem supporting torque induced by a given precentage change in the drill stem rotating torque. Each of these adjustments may be made independently of the other. As a result, the percentage rate of change in the -drill stem supporting torque may be substantially less than the corresponding percentage rate of change in the drill stem rotating torque, as is desired, and the mean drum torque may be readily adjusted to accommodate changes in the weight of the drill stem and/or the pressure of the drill bit on the bottom of the hole.

In the preferred form of invention illustrated in Figures 1 and 2, the variable torque transmitting device comprises an internal combustion engine, the output of which is Vconnected through a hydrokinetic torque converter to the drum.

lSince with such an arrangement the output speed of the torque converter is negligible during the drilling operation, the engine and torque converter will deliver a constant torque to the drum for any given engine throttle setting and that torque may be varied by adjusting the throttle position. Such adjustments in the throttle position are automatically made by an electrical torquepresponsive device associated with the rotary table drive. It will be noted-.that the value of the transmitted'torque is varied'by changing the speed of the source of power, and, consequently, the diiference between the input and output speeds of the torque converter. Anyrsuitable torque transmitting device capable of transmitting a torque which varies in accordancewith the difference between the input and output speeds may be used in place of thehydrokineticV torque converter. Examples of such devices 1in.- clude a hydrokinetic coupler and an electrical eddy-current coupler or clutch; however. a vjhydrokinetic torque .converter lis preferred -because of its torque :multiplication characteristics.

.As-sshown diagrammatically in Figure 1, a hoisting.drum I .isconnectedby-meanscfachain -2 and suitable sprockets to theloutputofa,changefspeed transmission, indica-ted diagrammatically vat 3. The input ofthe transmissioniS isconnected by .means ,of agchain 4to theoutputsshaft 5;of a hydrokinetic torque converter, Vindicated .diagrammatically at. The inputside of the torque con- .verteris :connected to `and vdriven by an internal .combustion engine i'I having an adjustable Vfuel feeding device, -indicated `diagrammatically .at 3. The adjustable fuel feeding l.device 8 ymayzloe the Y,usual :intake manifold throttle valve employed in spark ignition engines orfinthecase of diesel engines, may :include vthe `fuel injecter control mechanism.

The rotary table A9, `,which may be .of conventional construction and is effective to rotate the .drill stem ,during ,drilling operations, is ,driven .from .a .suitable .countershaft Ill by means of a chain '.izI and `suitable sprockets. The countershaft, in turn, is vdrivenby a chain :I2 and .suitable sprockets from ashaft t3, whichmay be .con- -nected to Vor disconnected from an alignedshaft .Mbymeansof apneurnatic clutch I5. The'shaft Ifmaybe drivenin any suitablezmanner bymeans of ia sprocket .I 6 Vveither ifrom a separate source Aof 4power or from the previously mentioned engine 1,

as desired. A.pneumaticallyfoperated brake 125 also mountedlon shaft I3. Associated withfthe countershaft =I. isa suitable induction coil, Vindicated .diagrammatically 'at I1 described, A pair of wires 2l and 22 extendsfrom vthe control box 20 to the adjustable fuel feeding device 8 of the engine 1 for the purpose of controlling the rate at which fuel is fed to the engine, as hereinafter more fully described. A third'pair of wires 23 and 24 extends from Vthe control box 20 to the solenoid 25 of a threeewayair valve 26 which controls lthe admission of air under pressure to the clutch I5. The lvalve 26 is connected 'to an air pressure supply vline 27 and is connected by means of a line 28, which communicates with a central bore in shaft I4, with the Aoperating mechanism of the Vclutch I5. The valve'normally connects the line 28 to an exhaust discharge line `or port 29; however, when the solenoid 25 is energized, the exhaust discharge .outlet is blocked and the Apressure supply `line 27 is connected to the line 28. The clutch I51is of thenormallyen'- gaged type and is disengaged when air is supplied thereto by means of valve 26. The details of construction of the clutch I form no part of the present invention and any suitable form of clutch may be employed. One suitable type is illustrated diagrammatically in greater detail in Figure 4, hereinafter described.

The control box iskprovided with three cone :trol knobs 35, 3;I yand 32. Afshereinafter set forth ingreaterdetair the control 'knob 36 adjusts the Y stemrotating torque at which the clutch I5 is automatically disengaged.

As Shown diagrammatically in Figure 2, the torque responsive device Il constitutes the pickup offa magneto -strictive ,torquezresponsiveelectrical circuit. While -any suitable form fof :pickup may ibefemployed for ythispurpose, the formillustrated ,comprises an Yinduction c 0i133 which surrounds .a ,portion of the countershaft it. The coil-'3B is connected :throughlinles :lili and Iig to aiccoil Bti whichis .inductivel-y coupled :to afcorrespcnding coll-.35 whichformsonelee ofia usual Wheatstone bridge, the other legs .thereof being providedwith impedances 36, ,3.1 and :3.8. Vr'Ehe input Vterminals 39 'and 30 of v:the gbridgematv I.be connected to :any Lsuitable source of 'alternating current by lines 4I 31H42.

Thenutput terminals t3 and-i-firofthetridgefare illustrated as .being Adirectly connected tol-the Vterminals of the primary winding of 1a transformer 45, although it will be understood that, if desired, an amplifier may lbe-inter-posed -betw'een the bridge and this transformer. 7|The output-.of transformer i5 is rectified, through a lpai-r of tusualrectiers 'E6 `and it?, and Ythe :rectified voltage `is impressed across ilinesrl and 49.

An adjustable portion of the V.voltage appearing between lines d8 andiig, which, as will be understood, is proportional to the torque-being transmitted throughcountershaftsI-Q, is utilized to con- .trol the'current iiow in the Apreviously identified lines 2i and 22, which .lines supply a-solenoid 5l)v which Ycontrols the position .of the throttle valve 5I the intake manifold 52 of the engine '1.

More `particularly, solenoid .50 Lis supplied with dlrect current througlra conventional rectili-er comprising rectiers 53 and 54, which are supplied with alternatingcurrent from transformeriii. As shown, rectier 53 is a diode, `whereas rectier 54 is o f the grid controlled type. vIt will be appreciated that by varying theilha'se of-the'alterhating current potential `impressed between the grid 5B of'rectier 54g-andi-ts cathode withrespect to that of the alternating current :potential irnpressed between its anode and its cathode, the magnitudeof current output of the rectier53-54 may be varied between relativelyfwide limits. Of course, if desired, both of -rectiersr53 and54 may be'triodes and the ,phases ofboth theirgrid's 'may Lbe simultaneously shifted with respect to ytheir cathodes.

Any suitable means 'may be utilized to variably control the just-mentioned ,phase relations. .The arrangement illustratedisconventional andicomprises a transformer 57 :having a'secondarywinding provided with a center tap which .s'idirectly connected to the cathode of .rectier 5L?. The .terminals of the secondary winding of the transformer '5l :are connected 'together `-by an impedance network comprising a resistor T53 lhaving a r.variable impedance 59 of the saturable reactor rtype. The junction 60 of elements 58 and 59 is Lconnectedto the grid 55 of rectifier 54 through 'a resistor Si and, preferably and as illustrated, -a lter condenser 62` is directly connected between the grid and cathode of the rectifier 54. It will be understood that by varying the impedance of element 59, the phase oi the potential of terminal 60, and, consequently, of that of the grid 56, may

be varied from an in-phase relation to the cathode potential to any desired degree of out-phase relation to the cathode potential, thereby varying the output of the rectier, as previously mentioned. The relative polarities of transformers 55 and 51 are such that the excitation of sole- Ynoid 50 varies inversely with respect to the impedance of winding59. i

, Changes in the impedance of element 53 are accomplished by variably exciting the direct cur- Arent `winding 63, which is connected across a resistor 54. Resistor t4 is directly connected in the -anode circuit of a usual grid controlled vacuum .tube 65, which is supplied with anode current from any suitable direct current sour-ce represented by conductors B and 61. The grid of vacuum tube 65 is variably connected, by the previously mentioned knob 3 l, to a potentiometer resistor 68, which, in turn, is directly connected across the previously mentioned lines 48 and 49.

The cathode of vacuum tube 65 is connected to one terminal `of a potentiometer resistor t9, which is supplied from a suitable direct current source represented by lines 'Eil and il. The previously mentioned knob 35 controls a movable tap '12,

which is also connected to one terminal of the resistor 68. The effective portion of potentiometer 69 thus serves to provide a bias voltage for the grid of vacuum tube 65, which normally maintains this grid at a desired negative potential with respect to its cathode. `As a result, increases in the voltage across resistor increase the current flow through tube E5 and winding 53 and thereby decrease the impedance of coil 59. This in turn increases the current through coil 5t).

VDecreases in the voltage across resistor 68 have the reverse effect. y

It will be appreciated that the above described f system will be so adjusted that for a given normal table torque imposed upon the countershaft It, the voltage imposed across the lines 2| and 22,

and, therefore, effective upon the solenoid 5B, will maintain the throttle valve 5l in a position which will result in the imposition of a torque on the hoisting drumV of the desired magnitude. More particularly, this normal torque of the counter- Y shaft ill, required to rotate the drill stem, establishes an impedance for the winding 33 which produces a normal amount of unbalance of thepreviously identied` Wheatstone bridge and causes the rectifier l5- lil to impress corresponding voltage across lines 48 and 49. A portion of this voltage, determined bythe setting of knob 3l, opposed-by an adjustable bias, determined by the setting of knob 3i), establishes a normal bias for the vacuum tube 65, which normal bias produces a normal current now through the saturating winding 53 associated with the variable impedance 59. This normal current flow establishes a corresponding phase relation between the grid and cathode voltages of rectier 54 and enables the rectier 53`54 to pass the corresponding value of current tothe solenoid 50.

The total drill stem supporting torque exerted upon. the drumffor `any given table torque applied :through .the countersh'aft lll may beadjusted by tuations ,rotation of knob 30. This results from the fact have a performance curve corresponding to that indicated by the line 73. This, however, is undesirable since it results in excessive variations in the drum torque for normal table torque iluc- By adjusting the control knob 30, the position of the performance curve may be shifted from that indicated by the numeral 13 to such curves as those indicated by the numerals 14 and l5, in which a substantial drum torque is imposed even though no table torque exists. since the magnitude of change in drum torque for a given change invtable torque is unchanged by these adjustments while the total drum torque is increased, the percentage change is altered somewhat. i

It will lbe noted that the slopes of the lines 53, I4, 75, etc., are determined by the setting of the knob 3|, which serves to determine the magnitude of change in drum torque for a given change in table torque. Thus, in order to reduce or increase the actual magnitude of change in drum torque for a given change in table torque, it is only necessary to adjust the position of the knob 3i. For example, if it is desired to obtain a performance curve corresponding to `that indicated by the numeral 1,6, it is only necessary to adjust knob 3l in a direction to reduce the amount of the total potential across lines 48 and 9 which is applied to the grid of tube 55. This increases the slope of the curve and the lateral position of the curve maybe varied by adjusting knob 3i! to produce any desired mean drum torque. i

It will be understood that the electrical control circuit connecting the pickup coil `ll with the engine throttle is, in itself, merely illustrative of one of many possible forms of measuring and amplifying circuits which maybe utilized to control the throttle position in accordance with variations in the torque transmitted through countershaft ii). Accordingly, other measuring and controlling circuits known to those skilled in the art may be employed in place of the type illustrated. In addition, it will be apparent that any form ofelectrical torque transmitting device may be substituted for the coil H. Thus, forexample, the coil i1 may be replaced by the familiar` strain gauge type of pickup which may be associated, in any desired manner, either with the rotating shaft It or, in accordanceA with conventional practice, with any member which is subject to a strain proportional to the table torque.

In some cases, for one reason or another, during drilling operations the drill stem becomes wedged by falling boulders or its rotation otherwise becomes blocked, with the result that the continued application of a twisting force to the upper end of the stem will cause a twist-off or breakage of the stem. In order to avoid this l'diiilcultm there is incorporated in the preferred -required to 'rotate the drill stem reaches a pre- However,

aesaoeo determined maximum value. This means is controlled by the same magnetostrictive pickup coil I1 which controls the position of the throttle valve 5|.

Thus, as best shown in Figure 2, the solenoid 25 of control valve 26 is adapted to be energized when current nows through the lines 273 and 24, which are extensions of the previously mentioned lines B6 and B7. The flow of current through the extensions of lines 66 and 67 is controlled by a vacuum tube 'l1 and` a pair of relays T18 `and 19. The coil of relay 'I8 is connected in the anode circuit of the tube Tl, which is of the usual grid controlled type` and which is supplied with current from the lines 66 and 61. The grid of Vacuum tube l1 is 'variably connected by the previously mentioned knob 312 to a potentiometer resistor 80, which, in "turn, is directly connected across lthe previously mentioned lines i8 and 49. The `cathode of vacuum tube Ti is connected to a suitable source 'of direct current potential, indicated diagrammatically at 8|, 'the opposite sideof which is connected to one terminal of potentiometer 8.0L This provides a bias voltage for the grid or the vacuum tube Tl, ywhich nor'- mally maintains this 'grid at a` desired negative potential with respect to its cathode.

The amount of grid' biasl suppliedY by the source 8l and the position of the knob 32 which vcontrols the potentiometer 8e' are so selected that when the torque'I 'transmitted through the countershaft |10 reaches a',v predetermined maximumk value, the current flowing through the anode circuit of the tube 'H will be just sufficient to close they contact 82S of `the previously `mentioned relay coil T8, this relay being or the type which does Vnot' operate 'until a predetermined Acurrent ows throughthe coil. Clos-ure of the vContact 32 energizes .relay coil 'I9 and thereby closes the vcontacts 8'3 `andV 84 associated therewith. Contact 83 is positioned ina holding oircuit vfor the relay coil 19; .and conta-ct Sli closes the circuit to the vvalve' 'operati-ng solenoid lines 23 and 24, thus energizing the solenoid 2l5= and shifting the valve 26 to the position in which it disengages clutch. I5.. This will immediately reduce the torque imposed upon the drill stem, but the resulting` reduction in torque will not deenergize the solenoid by reason of the fact that the holding circuit .for` the relay coil 'i9 remains closed- .even vafter the contact' 32 is opened. Consequently, the drive to the rotary table 9 remains disconnected until the circuit through the relay coil` T9 is broken by opening the normally closed .manual switchv d5 in the circuit of the coil 1.9. The torque at which the clutch i5 is disengaged by the rabove described apparatus maybe adjusted at will by means of the control knob. 32 of the potentiometer 80, which controls the amount vof potential across lines 43 and 49 whichiisimpose'd upon the grid of the tube TI. l

The detailed construction of the clutch t5 of Figure 1 forms no part of the. present .invention and, therefore, it maybe of any desired-:or `con ventional type. Thus.it may, `for example, be similar Yto the hydraulically `operated clutch .illustrated :and described hereinafter in connection .with the :form vof invention shown in Figurea During deep `rotary wellv drilling operations, the drill stem rotating torque .winds up .the Along l'drill stem toa substantial degree, Consequently, tif vwhen the table :torque'reaches a `maximum desired vvalue the ytable disconnected from v'the i drive engine by clutch I5, the drill stem will uritwist rapidly, thereby driving the table in reverse direction at high speed. Since this is undesirable, a brake |20' is provided for preventing such reverse rotation of the table driving mechanism. This is accomplished by connecting the operating cylinder |66' of the pneumaticallyoperated brake |2" to a pressure line 28. This brake mechanism may be of the type illustrated in greater detail lin Figures 4 and 6. The brake may .be released gradually to permit a slow unwinding rotation o-f the drill stem by closing a manual shut-01T valve |63 in line 21 and just cracking open a bleed-off valve |64' in line |65 'to the brake cylinder.

In Figures 4 through 7 is illustrated an alternative form of the invention, in which the variable torque transmitting mechanism comprises an 'infinitely variable positive displacement hydraulic transmission having means for maintaining the torque transmitted thereby at a substantially constant value so long as `the table torque remains constant. A torque responsive means is associ-ated with the rotary table drive for modifying the torque transmitted 'to the'hoisting drum in such a manner -as to produce a characteristic curve ofthe type indicated by the lines it, 'i5 and I6 in Figure '3.

Referring to Figure 4, the apparatus includes an engine B, the shaft Sli-of which is vconnected by means of a manuallyfoperated-clutch YS8 to a sprocket tt. The :sprocket y89 is connected by means of a chain 90 -to va sprocket L91| on the shaft of `a positive variable displacement pump S2. The pump $12 is connectedto a'positive displacenient pump 93 by a low ypressure `line -9'4 and a high pressure line 95. The output fshaft of the pump 93 is connected .by a sprocket '85 and a Vchain sito a sprocket Baron the-drill stem hoisting drum B9. -Any suitable torque multiplying device may be incorporated inthe connections between the sprocket 96 and fthe Ydrum '99, as desired.

The shaft -8-'1 of the engine '86 is also connected by means of a hydraulically operated clutch |00 to the input shaft lol of "a dinerential mechanism, indicated generally at |02. 'The clutch IBB is `normally engaged'but'mayibedisengaged by the application of iluid'under pressure in pipe 163. Thus, asshown more or less `diagramrnatically,'theclutch |00 includes a plate |915 xed to the shaft vlil and a plate itwhich is splined to the shaft 87. Plate |65 hasa rearl-vvardly directed annular flangefforminga cylin- `der which receives a piston lil'xed to the shaft Y87. The right-hand end of the-'cylinder is closed 4by means of a plate'ldi. Operating iiuid is ad- `mittedto the space betweenthe piston |66 and ithe right-#hand end of thecylinder 'by vmeans of "a passageway-through Vthe shaft A81, indicated in dotted linesat |98. This passageway communi- .cates Vwith the interior of van annular chamber :in a stationary member |09, zwhich surrounds :thcshaft 31 Vand is connected .to V.the previously mentioned pipe |63. Springs lganormally hold the clutch engaged,but, on applicationof fluid `under pressure to'thepipeililgthe clutchplate |05 is retracted tothe rightmndthereby disconnects thev drivezconnections'between `the shafts 8'! and |'0 The .differential mechanism ||12may be `of ,any suitable type but, :as `illustrated, comprises a 4housing I I0 which -supports and' journals: an` output :shaft rand-a .tubularrtorque' reaction :shaft A l2. Shaft |-0 Igpasses throughzthe tubulartsha'ft 9. l|2 and'is journaled for independent rotation therein. The inner end of the shaft |01 carries a spur gear ||3 which meshes with a plurality of planet gears ||4 journaled on the tubular shaft ||2 and meshing with a ring gear ||5. As a result of this construction, torque may be transmitted through the diiferential from shaft 9| to shaft it being understood, however, that shaft will rotate in the opposite direction to that of shaft |9| so long as the tubular reaction shaft ||2 is substantially stationary. In addition, it will be appreciated that there will be transmitted to the tubular shaft ||2 a reaction force proportional to the torque transmitted to shaft This reaction force, as hereinafter pointed out in greater detail, is utilized to control the r torque transmitted by the hydraulic transmission 92-93. i

The output shaft is connected in any suitableV manner, as by means of sprockets ||6 and ||1 and a connecting chain IIB, to a conventional rotary table H9 adapted to rotate the drill stem during the drilling operation. AnyY suitable speed ratio change devices or reverse gears may be incorporated in the drive between the shaft ||I and the rotary table, as desired.

, Mounted on the outer end of shaft is a brake drum |29 which, as hereinafter pointed out, is adapted to hold the shaft and, therefore, the rotary table against rotation under certain circumstances. n

In accordance with conventional practice, either one of the positive displacement pumps 92 and 93 may be provided with means for varying its displacement from zero to a flow of any ,desiredV magnitude in either direction; However, in the preferred form ofapparatus illustrated diagrammaticallyin the drawings, only the pump 92 is of the variable displacement type,

the pump 93 being a constant positive displace-1 ment pump. o

While any desired type of positive variable displacementA pump may be utilized, one satisfactory type of pump is the wobble plate type pump. Both of the pumps 92 and 93 may be of the same type, but only pump 92 need have means to adjust the angle of the wobble plate to vary its displacement. Since the detailed construction of the hydraulic pumps 92 and 93 may be conventional and forms no part ofthe present invention, no further illustration and description are necessary. It is sufficient to note merely that when the wobble plate of pump 92, indicated fragmentarily at |2| in Figure 5, lies in a plane at right angles to the axes of the pump cylinders, the displacement of the pump is zero and, consequently, rotation of thepump shaft by the :sprocket 9| `will not result in the flow of any liquid through the pump. When the angle ofv the wobble plate |2| is shifted in one directionV from its Zero displacement, flow will occur in one direction; while a shift of the wobble plate in the 4opposite direction fromthe zero displacement position will result in flow through the pump in the opposite direction.

The two pumps 92 and 93 are so connected hydraulically that the shaft of pump 93 will rotate in one direction or the other, depending upon the direction of flow of the liquid through the `pumps 92 and 93, and will remain stationary when no flow occurs through the pumps. As a result, during thedrilling operation the weight of the drill stem supported by the khoisting drum 99 in the usual manner will be transmitted through stresse@ 9S and L$8 to the `slflaft of pump 93 and develop a back pressure at the high pressure side of pump 93 which is proportional to that portion of the Weight of the drill stem which is supported by the hoisting drum. This pressure is transmitted to the pump 92, and connections are provided for adjustingthe angle of the wobble plate |2| in pump 92 to maintain the pressure developed by pump 93 at a substantially constant value, regardless of the direction of rotation or the speed of rotation of the hoisting drum. Therefore, except as'hereinafter pointed out, the hydraulic transmission always tends to support a fixed weight, regardless of the rate of progress of the drilling operation.

The means for controlling the pressure developed in the high pressure line 95, which oo nnects the pumps 92 and 93 in order to maintain that pressure at a substantially constant value, is best shown in Figure 5. As there shown,the

"wobble plate |2| of pump 92 is connected to a differential double-acting piston |22 by means of a ball and socket joint, indicated generally at The piston |22 is slidable in a cylinder |25, the large end of which is connectedby a conduit |25 to a port |26 in a pressure control valve |21. The small end of the cylinder is connected by a conduit |28 to the high pressure line 95, as best shown in Figure 4. A line |29 also connects the high pressure line to a port |39 of the control valve |21. The pressure control valve is supplied with a third port |3|, which is connected by means of a line |32 to the low pressure line 94.

Valve |21 includes a spool having a pair of lands |33 and |34. A coil spring |35 normally urges the valve toward the left, as viewed in Figure 5. Land |33 is adapted to control com-v munication between conduit |25 and the conduits |29 and |32. Since the pressure existing in the high pressure line 95 is in communication with the left-hand side of the spool, the spool will assume the position in which that pressure balances the force exerted by spring |35. When that position corresponds to the position illustrated in Figure 5, port |26 is `closed `by land |33. Consequently, the right-hand end of cylinder 24 is in communication with the high pressure line 95 Vand the fluid at the left-hand end of the cylinder I 24 is trapped. This locks the wobble plate 2| in whatever position it assumes at the time the spool of control valve |21 reaches the position illustrated inthe drawing. In the event that an additional torque is imposed upon the pump 93 by the hoistingdrum 99, the pressure in line 95 will tend to increase, thereby shifting the spool of valve |21 to the right, as viewed in Figure 5, against the action of the spring |35. This permits fluid to flow from the line |29 through the valve and line |25 to the left-hand end of cylinder |24, thereby shifting the wobble plate to a position in which it permits a greater flow of liquid through the pump 92 in a direction from the line 95 to the line 94. It will be apparent that this increased flow through pump 92 (which is then acting as a motor, driving pump 93) increases the unwinding speed ofl the drum 99 and, therefore, causes the drill stem to apply greater pressure to the bottom of the hole. This reduces the amount of weight of the drill stem which must be supported by the hoisting drum 99 and, consequently, reduces the pressure in line 95. As soon as the pressure in line 95 reduces to its original value, the spool of valve |21 will return to the position illustrated and thereby hold the wobble plate |2| in its- 115 nevv.-v positiormofgadjustment.;l Accordingljh, the valve ,I 2 'l servesvtoimaintain-.thefpressure :im linel 95-at a .constant value and, therefore;. -the torque; exerted by the pump; 93 .von -theadr-urm remains..Y

at a constant value. Thisvaluemaybeadjusted 5K1 by adjusting' the gtension of. spr-ingj 35 and. means are provided Yfor-.-so'varying-fthe tensionof: spring; I35 vas-.to vary the pressure in line-.IlEr-and,` con-.- sequently, the ,hoisting drumtorqueto produce4 thedesired changeszin'. .the fsupported Avveight of 10 the drill stem previously described.

Thusfas shown inFigures ftandz, thefreargend. L of the spring-135 seats against-aplungenIthef position of which: .-is.-,controlled by a. sliding-stem t Il- An .adjustable capnutfISBlris threadedon l5*5 the endVV offstemv` I 3l and` bears ,against 1azfcain il 39 which-as best showninfFigures 4 andi?, is :iixedA to the tubular .torquereaetioneshaft I I21ofV .the :1 differentialI mechanism I 02;. Itwv-ill :be enoted, as 1 best shownin-Figure 7, that the.. controlfvalved 2l f 20 4 is mounted onv a bracket Y I IlIlisecured:tozthe-r cas;

ing I Ill of :theediierentiallmechanismx 1f i' thee` input shaft I6 I# of the e diierentialxis;` rotated"` clockwise; :aszviewedzin Figure i7, aslisenormahthe; torque reactionn exerted .on' theeI tubular? shaft 1 25 I I2 and, therefore; on .the cam :I392tends :tosvving the cam finagclockwise fdirectionr. Rotationfof 5. the'camwis re'sistediby. meansoia relatively heavy.D coil spring,` I I I lone end .off.:.whiolniszconnected;

tolthe camrandftheotherito a stationaryzbraclet' 30.

I l2 by means :oi anceye-bolti: I 43 fand aitpaimofa.; adjusting;nuts H4451. Imorder tecdamp'enzthe: movements of the cam ISS, the cam isiconnectedi` to the casing 'f of :I theiv-.diferentalmby means, of a; doublefactinggdashpotztl 45,

The roperationiof the mechanisnr-so1faridezpscribedlis 'as'follo'wsaI Asepreviously indicated; the I, control valveaI 27 lnormallyoperatesito maintain the supportedi'v/eightliof dhezdrill stemcata cone.l stant V value :independent of theaspeedof Totati'on i 40 ofthe hoistingfdrum Thatlvaluezisdetermined.' for any rgiven" drillfstem :rotating: torque :transeY mitted th'reuglrthe-idile'rential'y I 023cv l:the adjust; ment lof ithe fnut f I 38 :ont: the valve plunger I 'll Toffacili'tatesuch; adjustment; the cap nut .1I 38e 45 is preferably-i maderas the:hubofiaehandzlvvheel It; as best. shuvvn: inLFiguree'l Any :fsuitable:v means, suc-h; as aglocl nutl l-'L'mayxibe zernployedi1 to locklthe ehand Wheek Lin any 5 desired adjustedz.E position.; Itswill; bei understood. that :this: ader 50 justment willbechanged `from-time to time .asthez weight i of the .1 drill.' stem i increases during; the; drilling .'operationz. So: long: a asethezitorquei; ree'` quired to11otateithe drill .stemiremains constarm: thezcarn I3Siiwillzremaimstationary and, .conscev 2 55 quentljzf ,the :I torque i on; the drillif. stema will; ree main constant. In the:leventz'offranincreaseein; the torque required .'.tolzrotateethetdrll .stem-whe i, torquereactionexertedzonsthe cam-LI 39 Will Etend to rotate .thefcamqin amclockwise :direct-ion,as 60 viewed f ixr Figuree- 7 ,y thereby ,f compressing; the:y spring I 35 -andf-,causinggthe contro1.1.valve; I 2 to. balance the system .at afhigher pressurein ,thev line .95 and,therefore;Witlrarigreater. weight supfA Y ported by the hoistingg'drum: 99 andless-Weight. on 65.

the :bottom .-of- .the, l1ole.-'; Reductionsiin :the-edrill. stem rotating forcee-Willi havefthe :reversefeecti Inforder toproducethe desired result, the mecha-n nism Vis sofA designed-fthatethef percentage magniftude'of change-inrthefdrillzstem supportingtorque. 70s

on. the hoistingadrumr alisrsubstantially;lessthan' the .percentagesmagnitudeof change .ina,-;thefdrill stem;rotating torque whiclizzcausedrthat :change inrthe 'drumftorqueg' thus producing.'- acharacter-` stc;cur.ve of..E the general ytype'.:indcatedi by the` 75 ty j per cent ,change :in ,the.,.table `torque Vmay eiect...only.,.ve perrcent or.. less vchange .in .the

drumtorquei.

in the table torque,.aespringhaving adiierent characteristic mayjbe` substituted either for the spring 35 or spring Idl., or, as is preferred, the slopezofthecam.lI39.-is .adjusted to. change the travel. of; rod-I Y,I 3ft .for.;af,given .angular movement of the :came This fis;` accomplishedv :by pivoting thecam,-near onefendibyv-means of a .-.bolt 48 I 5.l '.'extendsfthroughan opening in :arm I e9 and' a..slot yI5Iin;the cam-adjacentits opposite endf and serves to .clamp thecamin any Adesired angu-.

lar position of adjustment.

It :will ybe; apparent .-from.: the above Y that the ing/torquefbyfaegivenfchangesin the-.table torque, maygbefreadily-adjuStedby-means of :hand Wheel f; E46 @and thefadjustablewcam .|39 `to produce van;7 desired.iperforma-ncefcharacteristic curve. Conmayfbe utilized to.:perform' the samefunctions as that 'previously,describedintconnection with Figures-..1 zand 12.2. The ediierential gear .typeef torque responsive element disclosed in'Figurefll.

is fpreferredforuse -in Lconnection .with` the positive-displacement"hydraulicetransmission Vfor the reason that 4rit :can:;.be easily designed to `deliver the:.,-rather:substantial force requiredto control tl'1ef.valve-.-I2..A It Willbe appreciated.however;v

that "r any f othercfformoff: torque l f responsive devicefinrthertablef; drive mayfbe substituted for' the .l differential mechanism; Thus; the :form oi vtorquea responsive-f: device sdisclosed. in Figures 1 and 2 may be substituted for the differential mechanisme.. or vice; :versa:y

Thezmechanismfor-zdeclutchingthe table drive whenv the "table: etorque.: reaches :a predetermined maximum;Y value: is: best; shown in. Figures 4 throughY :7; As .:there shown, `thepreviously mentionedppipe I 03Iis connected tor theldischarge portV I 52 of: :a;.contr.ol ';valvee I 53,? andi.'` the :inlet 4port 1 I5-of 4the-.control val-veais connectedby means Vrof.:a line- .-I55.1to;the high .pressurellnezgx .As-bestv showrrinlgurezfl; 'thefvalve .I 53 `is proL vided with :a/,plungerl 56 "Jvvhichzis .urged .at allv times rbyga lightspringil'i iin a dr'ectionto close theport I52.. The ,valvezplunger is :provided with anf .operating-stem. :I 5B zV of=5small`er :diameter than' the sporti'v I 52;: .with :the :resultL-that l:the pressure applied to: theav interior of? thevalv'e. housing through line..l-assiststhe1sprin'gfI5'I in hold# ing thewalvefclosed." The-stem .I5Slis connectedv byyarlost motion,connecti`on I59Ito, a` rod I6Il which; initurn; connected: by: means of a` turnbuckle IGI :toranralignedzrod: I 62 that is pivotally:connectedtoztheiarmd 49 of 'shaft I I2 The adjustment of the turnbuckleal 5 I. .andthe .length of the slot in the lost motiorrzc-onnection IES areisuchethat theevalvelfl 53 .remains iclosed until the;torquea'eaction;on.thleshaft :I I2 rotates that shaft tothemaximum4 desiredgdegree:in4 a clockwise direction;as;'viewedlainL/Fgure ..'7, at Which theivalvplungerz'l gandtherebytransmit fluid under ,pressure to zthel: line :I 03. This ,disengages the .clutch=;.; I G...

It 'will benobservedtthatronce the valve plunger I56`sis unseated;.thespressureactng on the left-l In order te permit .anadjustment in the rate. oilvchange in the drum .torque .for algiven change mean drillstem.supportingtorque imposed. upcn the :hoisting;r drum, vasjwellas :the percentage rateof fchangeeinducedx. in the dri-ll .stem support- Y time r;the;moven:1ent of the'ashait II2 Avvill unseatv light so that it does not overcome this tendency. y

Therefore, once theV valve has been opened by clockwise rotation of the shaft ||2, it will remain open, regardless of the position of the shaft.

In order to close valve |56 when desired, it is necessary to close communication between the valve and line 95 by means of the hand valve |63and open the hand valve 64 Which connects the interior of valve |53 to the low pressure reservoir or the low pressure line 94. This relieves all of the pressure acting on the valve |53 and permits the spring |51 to rseat the plunger |56 and thereby close the discharge port |52. As soonas the valve |53 is closed, valve |63 may be opened and valve |64 closed to restore the mechanism to normal operating condition.

Means are provided for slowly releasing the brake'band |61 to permit a gradual unwinding of the drill stem. This is accomplished by connecting thedischarge port of valve |53 by means of `a line |65 to the operating cylinder |66 of a hydraulic brake mechanism, shown best in Fgures 4 and 6.` This mechanism includes the previously mentioned brake drum |28 on shaft a brake band |61, a brake operating lever |68 and a piston |69 in the brake operating cylinder |66. The cylinder |66 may be pivoted by means of a pin to any suitable support and contains a spring |1| which normally holds the brake band |61 in a disengaged condition. It will be apparent that when valve |53 opens, piston |69 will move to the left, as viewed in Figure 6, and apply the brake, thus preventing the previously mentioned reverse rotation of the table incident to the declutching of the table drive. The brake band |61 may be released gradually to permit a slow unwinding rotation of the drill stem by closing the previously mentioned valve |63 and just cracking open the drain valve |64 to permit a slow bleed off of the pressure in cylinder |66. y

It will be appreciated that the brake mechanism employed in the form of invention illustrated in Figures 4 through 7 may be incorporated, if desired, inthe form of invention illustra-ted in Figures 1` and 2.

In Figures 8 and 9 is diagrammatically illustrated a further form of the invention inwhich a variable torque transmitting mechanism comprises an engine driven externally excited eddy current .clutch and in which the torque transmitted to the drum by the eddy current clutch is controlled by a torque responsive device in the table drive which is effective to vary the external excitation of the `eddy current clutch. Thus, as shownin the drawings, a hoisting drum |12 is connected to the output shaft |13 of any suitable form of change-speed transmission iN. The input shaft |15 of the change-speed transmission is connected to the inner member of an eddy-currentclutch |16, the outer member of which is connected tothe shaft |11 of an engine or motor |18. It will be understood that in accordance with conventional practice, either the4 inner or the outer member of the eddy current clutch |16will be provided with a suitable fieldV which, sincethey will be'cutting the lines of' force produced by the exciting field, will transmit an electromotive force from one of the clutch members to the other. Consequently, for any given excitation of the eld coil |19, the torque transmitted from the shaft l|11 to the shaft |16 will be proportional to the difference between the speeds of those shafts.

shaft Iii is driven by the engine or motor lis Y at a relatively high speed in the direction indicated by the arrow thereon, while shaft |15 will be rotated in the opposite direction during normal drilling operations by the unwinding rotation of the hoisting drum |12. The speed of rotation of the shaft |15 incident to penetration of the drill lbit is relatively slow even though,

substantial torque multiplication is provided by the transmission |14. In accordance with the present invention, the speed of shaft |11 is made so much higher than that of the maximum speed of shaft |15 in a reverse direction that variations y in the speed of shaft |15 incident to variations in the rate of drill bit penetration will have a negligible effect upon the difference between the `speeols of shafts |15 andv |11. Consequently, for

a constant speed of Vshaft |11 and a constant excitation of coil |19, the torque transmitted to the drum |12 remains at asubstantially constant value. This value is so selected that it supports 1 all of the Weight of the drill stem except that portion necessary to provide the desired pressure of the drill bit on the bottom of the hole. The mean value of this torque may be adjusted by adjusting the speed of the engine or motorl |18; 1f an internal combustion engine is used, that adjustment'will be effected by changing the posif tion of a fuel feeding control device, such as an intake manifold throttle valve.

The rotary table |88 is driven in any suitable manner from a second engine |8| through a differential` mechanism |82 similar to the difieren` tial mechanism |02 previously described. The tubular torque reaction shaft |83 of the diiferential |82 is provided with an larm |84 which is l connected to a stationary bracket |85 by a heavy coil spring |86 which resists clockwise rotation of reaction shaft |83 in response to table torque reaction forces. Consequently, the angular position of the arm |84 will vary in proportion to y clutch |16 and thereby vary the torque trans-- mitted to the hoisting drum. The mechanism is so designed that substantial percentage increases in the table torque 'will effect mino-r percentage increases in the drum torque transmitted through the clutch |16, 'and vice versa.

With the above described mechanism, thetcrque transmittedl to the drum for any given table torque may not only be adjusted by adjusting the speed of the engine or motor |18, but

y may also be adjusted by adjusting the turnbuckle 7 o |88. Inorder to adjust the percentage rate of change of the drum torque for a given percentage change in the table 'torque, it is only necessary to connectthe linkage |81 to the arm |84 at any one Yof a plurality of points spacedv radially from the axis of the shaft |83. For this purpose,

aie-sages;

a^- p luralityfof j apertarese` leap-is providediin. the-..2 armifl .fior the reception offa bent end of the.

While a diierential torque responsivesmeans is employedin connectionwithgthe mechanismof Figu1'es ;8,and; 9,it will be apparentpthat the eld excitation of clutchfl lgmay becontrolled bythe electrical torque responsive apparatus of Figure 2, in1vvhich event vthe coil. 50 of Figure 2 will bathe field coil offthey eddyjcurrent clutch Hr, More-. over, if rdesiredfthe dilerential mechanism of Figure l9 f and` its ,associate.d flinkage l 81 emav be connected ;directlyto;v the Yengine throttle 5i of Figure- 2in lieuofthe electrical torque controlled' device -there disclosed,- or;;the diiierentially con;-

trolledvariable `resistance]Sill-of Eigures and 9 f may beutilizedf tocontroltheow f current in thexthrottle-.control solenoid oFigure 2 :Without departing i' fronr.A the spirit orrscope of i the in:v

While several .forms eofithe invention :haVebeen illustrated and describedlierein, V4it :will `be appar ent that variationsiinztheeconstructiongand ar rangement of partsvmaybe indulged in without departing from .the spirit ofethe invention or the scopeaof the appended-f claims.

1 Rotary Well drilling; mechanism including meanseto. rotateftheedrill stern, an enginerdriven variable positiver; displacement hydraulic transmission .forexertingja drill stem supportingi force proportional tothe hydraulicpressure developed in` saidtransmission-, hydraulic ineans ior; varying the.; speed.; ratio VAot said4 transmission, a control valve mechanism for, said hydraulic means re- Y sponsiveto thefpressuredeveloped vin said transmission :for maintainingsaid D lessure at a substantially constant value by adjustmentof said.

speed ratiofsaid control valve mechanism includinge means for; exerting afsubstantially constant biasingiforcepnsaidfcontrol valve in the direction ofy actuation which tends to increase the hydraulic ypressurerin saidtransmissiom means for.

applyinga forceron said'valveina direction to oppose-said biasingmeans and -Wh-ich Varies in magnitude with .thefihydraulie;pressure in said transmission,` anda torqueresponsive apparatus.

operativelyconnected to said drill stem rotating means.fandiEconnectedto said l:|iasing,1r means for increasingthe force yexerted by said biasing means on said-fcontrolvalve byan. amount Whichis approximately .proportional to the torque required to rotate thedrill stem,

2.Rotary Well drilling mechanism including means to rctate,-the drill stem, an internal coin-v bustion :enginehavingjjmeans :for controlling the rate o f\ fuel consumptionrlan eddy current clutch..

having-its pinput shaft .connected to the engine, a l1oistingdrum connected to the output shaft oisaidclutch` and adapted-to support a portion of Vthe :weightof the dril1 stem, said clutch having an -externally excited iield coil, means for var-,ying theelectrical current new through said eld coil, and a torque responsive apparatus operatively;connectedtmsaid drill Astem rotating means and connected toisaid current :dow vary--A ingmeans forincreasing the `current in Ysaid coil byv an amount approximately .proportional to" the Y torquesrequired to :rotate the drill stein.

3. Rotary Welldrilling mechanism including drive -means for rotatingzthe drillstem, a disen-l gageable clutchrinlsadffdrive -.means, a hoisting drum for suppOrting yaiportionoi` the `Weight 4of the dril1 stem, torquetransmittingmeans capableI Oft-transmittingetc the 1drum a substantially con-` drive means ifor;rotating the gdrillstem, a disen-` gageable clutch insaid drive means, aV brake. adapted j on; engagement to. prevent f rotation -ofsaidl drillgstemi. aghosting drumyfor; supporting a portionpothe weightzof thedrill stem; torque;-

,z transmitting j meansr capable of transmitting; to

the drurn;a substantially' constant torqueyvhich,` is .independentpofvariations in the speedfofthe s drum; incident to .changes in :the rate of. .'drill bit penetration; control:means' for adjusting theyvalue of theztorquegtransmitted:by said means,

a torque. responsiveapparatus voperatively connected to.. said z. drill stem rotatingmeans and connected 'no-said control; means orgincreasings; the torque applied` to said. drum by said.` torque.Y transmitting means :by an; amount `vvhiclrzis ap V proximately: proportionallto the torque required t' to rotate .the 'drill stem,i and;means foitdisengagf ing said clutchand engaging-said brake whenthe f. drill stem rotating :torque 1reaches-xa; predeter; minedvalue;

5. In arotaryzwell 'drilling mechanism, meansfor rotatingthefdrill; stem including a. disengagef.v able `clutch in thedrive connectiom means for i disengaging said clutch when?thetorquesrequired. torotatethetable reaches a predetermined value. aptorque responsive apparatus operatively con- .r nected to, said. drill 'stem rotating .means and Vto said clutch disengaging means for actuatingthe clutch disengaging means when the torque .re quired to rotate: the table. reachesaepredetermined value, and means for preventing reverse rotation lofthe uppenend ofethe drill stem when said clutch-is disengaged.

6. Rotary Well drilling mechanism,. including` means torotate thev drill stem, an engine-driven variable;positive.l displacement hydraulic transmission-forcxerting a drill stem supportingforce: proportional tocthe. hydraulic f pressure developed in said .'transmission,.hydraulic 4means for-varying 1 the :speed `ratioor said:` transmission; a control. valve -rnecha-nism-pfor said hydraulic f means re sponsiveto-'the pressure developed 'inf said trans,- mission forv maintainngjsaid vpressure .1 at 1a sube stantiallyconstant value-byradjustment of said". speed ratiofsaid: control valve mechanism including means forexerting; a substantially constant biasing forceon: said control valveinithe direction Whichntends vtaz/increase the Vhydraulic :presfsure -in said transmissiomnieans for applying a' force onysaid valve in a: direction to oppose-said: biasing meansand which varies in rnagnitudeA with the hydraulicgpressure insaid transmission;. and a torque responsive apparatus operatively connectedato saidV drill stem. rotating-.means and; connected to saidvalve mechanism 'for increasing; the total biasing force onfsaidfvalve in'said d irec tion., by, an. .amount approximately proportional: to the torque requiredftdrotateathe drill. stem..

7. A,V p owergtransmission.. system for use-Av in -y rotary We11' dr il111g. includng -.a hoisting; drum-v c ....17 for sustaining at least a portion of -the weight of the drill stem, a driving member for rotating the drill stem, a. torque transmitting mechanism connected to the hoisting drum, control apparatus for maintaining the torque delivered to the drum by said mechanism at a substantially constant value which is independent of variations in the speed of the drum incident to changes in the rate of penetration of the drill bit, means connected to said control apparatus for adjusting the torque maintained by said control apparatus, a torque responsive apparatus operatively connected to said driving member and responsive Ato the torque transmitted through the member and connected to said adjusting means and continuously operating on said adjusting means to increase the' torque delivered to the drum over that maintained by said control apparatus when no torque is transmitted to the stem by said member by an amount whichv is approximately proportional to the torque required to rotate the drill stem, and a second adjusting means associated with said control apparatus for adjusting the torque delivered to said drum by said mechanism independently of changes in the torque required to rotate the drill stem.

8. A power transmission system for use in rotary Well drilling, including a hoisting drum for sustaining at least a portion of the weight of the drill stern, a driving member for rotating the drill stem, a source of motive power, ak torque 'transmitting coupling having its input connected Y to the source of power and its output connected to the hoisting drum, said coupling being of the type 'which transmits a torque that varies with the difference between the speeds of the input and output, control apparatus for maintaining Number the speed of the Vpower source at a substantially constant value, means connected to said control apparatus forV adjusting the sp-eed maintained by said control apparatus, a torque responsive apparatus operatively connected to said driving member and responsive to the torque transmitted 'through said member and connected to said adjusting means and continuously operating on said adjusting means to increase the speed of the power source above that maintained by said control apparatus when no torque is transmitted to the 4stern by said member by an amount which A'is approximately proportional to the torque required to rotate the drill stem, and a second adjusting means associated with said control 'apparatus for adjusting the speed at which the power source is maintained by the control means independently of changes in the torque required to rotate the drill stem.

CHARLES M. OLEARY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS y Date 

